The present invention relates to a web fed offset rotary printing press and more particularly to a multiple-purpose offset rotary printing press capable of being adapted for printing of a very wide range by the method of switching between two different printing modes in the single printing press, for example, quadruplicate printings on one side of a web, triplicate printings on one side and monochromatic printing on the other side, duplicate printings on both sides of a web, duplicate printing on one side and monochromatic printing on the other side, and monochromatic printing on each of both sides of two webs respectively.
Constructions and operations of well-known offset rotary printing units are divided into the following classes according to the arrangement of cylinders thereof.
(1) A three cylinder train unit in which a blanket cylinder is between a plate cylinder and an impression cylinder and contacts with both of them, to afford a monochromatic printing on one side of a web.
(2) A four cylinder train unit in which a pair of blanket cylinders mutually contacting are between a pair of plate cylinders cooperating therewith and contacting therewith respectively, to afford a monochromatic printing on both sides of a web by feeding the web between the blanket cylinders. This is called a blanket to blanket design.
(3) A five cylinder train unit in which a common impression cylinder is between a pair of the blanket cylinders of the four cylinder train unit, to afford duplicate printings on one side of a web. This is called a satellite design or a common impression cylinder design. In case of adding a third or fourth blanket cylinder in contact with the common impression cylinder, this affords triplicate or quadruplicate printings on one side of a web.
(4) A printing unit capable of switching between the four cylinder train and the five cylinder train, is described in French Pat. No. 1,257,552 and U.S. Pat. No. 3,329,086. This can be used in two ways, whereby one is used as the four cylinder train unit and the other is used as the five cylinder train unit by the method that the pair of the blanket cylinders are switched between a first position i.e. the four cylinder train in which they make contact with each other, with their respective plate cylinders and are isolated from the common impression cylinder and a second position i.e. the five cylinder train in which they are isolated from each other, make contact with their respective plate cylinders and with the common impression cylinder. This unit can afford a monochromatic printing on both sides of a web or duplicate printings on one side of a web.
Now, using the above described printing units, if it is desired to be adapted for multiple-purpose printing including quadruplicate printings on one side of a web, triplicate printings on one side and monochromatic printing on the other side, duplicate printing on both sides, duplicate printing on one side and monochromatic printing on the other side, and monochromatic printing on both sides of two webs respectively, it is required to have either twelve cylinders consisting of four juxtaposed arrangements of the three cylinder train units as described in the item (1) or ten cylinders consisting of two juxtaposed arrangements of the switching between four and five cylinder train units as described in the item (4).
However, the former requires a greater quantity of cylinders whereby a large space is occupied so that it would be expensive. On the other hand, as the latter requires a pair of mechanisms for switching between the position where the pair of the blanket cylinders mutually contact and the position where the blanket cylinders are separated from each other and contact with the common impression cylinder, it is easy to make a mistake, while the operation for switching and construction thereof is complicated and expensive.
Further, as the latter has the single and common impression cylinder which separates from and contacts with the pair of the blanket cylinders, not only it can not help making short the length between the two extreme positions in which the pair of the blanket cylinders are bodily moved, but also it requires a rotative movement of one of the pair of the blanket cylinders in reverse direction when they are switched from one to the other position.
Therefore, it is impossible to achieve the complete separation of engagement of gears from each other by the limitation of the movement only in the direction along the faces of the gears, so that the well-known device has been designed so as to be more movable in the direction along the axes of the gears. Further particulars in connection with the above description are indicated in the U.S. Pat. No. 3,329,086 and Japanense patent publication No. 51-14922 corresponding thereto. That is to say, the latter comprises the complicated geared reversing mechanism including more shifting in the direction along the axes of the gears, the pair of the switching mechanisms for each pair of the blanket cylinders having the geared reversing mechanism respectively.
Furthermore, the well-known switching mechanism for the pair of the blanket cylinders has been achieved by a method in which the shifting of the blanket cylinders from one to the other positions is made via the intermediate mode, i.e. the state of the impression throw-off. This inconveniently requires two reciprocating motions of the actuator, as well as a conversion of the fulcrum of the power transmitting link at the intermediate mode. As a result, the conventional system requires a troublesome operation which may incur an error.